Climate Study Links Human Activity to More and Stronger Cyclones in Southeast Asia

The first tropical cyclone to strike Myanmar and Bangladesh this year - cyclone Mahasen - destroyed thousands of huts and forced up to a million people to flee their homes last week. A Utah State University-led research project has found that tropical cyclones that threaten millions of people in countries surrounding the Bay of Bengal each year are likely to increase in number and intensity.

Mahasen killed 18 people, but the worst of the storm skipped Myanmar (Burma). Though the cyclone weakened as it made landfall, there was still severe wind damage and flooding, and it is only the beginning of this year’s tropical storm season in the region.

Research on intensified cyclones was led by Simon Wang, assistant professor in USU’s Department of Plants, Soils and Climate and the Utah Climate Center, and was part of NASA’s Energy and Water Cycle Study. The researchers found that the number of spring cyclones over the Bay of Bengal has increased since the 1970s, and that more cyclones grew to hurricane force. The number of hurricane-force cyclones that have made landfall in Bangladesh or Myanmar during that period has doubled. Myanmar was hit by major cyclones three times in a four-year period, including Nargis in 2008 that caused destruction comparable to the tragic 2004 tsunami in South Asia.

The research team, which included scientists from Columbia University and the Pacific Northwest National Laboratory (PNNL), determined that the lowest portion of the Earth’s atmosphere, the troposphere, which contains nearly all the atmosphere’s water vapor and airborne particulates, has expanded and become warmer over the Bay of Bengal and caused the sea surface temperature to rise.

“We found that the troposphere over India and the Bay of Bengal has expanded, leading to a stronger monsoonal circulation that favors the growth of tropical cyclones and severe storms,” Wang said. “This trend may also have contributed to the deadly tornado that occurred in Bangladesh on March 22.”

The study, recently published in the Journal of Geophysical Research, found that this regional climate change can be explained by two manmade phenomena: increases in the amount of fine, airborne particulates from dust and burning carbon-based fuels like oil, coal and natural gas, and sea surface warming that is the result of increased greenhouse gases like carbon dioxide.

"The amount of greenhouse gases and small particles emitted by human beings by fossil fuel burning has been rapidly increasing over India and China in the recent years," said atmospheric scientist Jin-Ho Yoon at PNNL. "We believe that the change in tropical cyclones is caused by continental-scale response to these increases."

The researchers also found that the onset of the monsoon season in Myanmar has advanced by five to ten days since 1979. That information is significant for agricultural planning in a country that is highly vulnerable to extreme weather systems because it is just beginning to recover from decades of civil war and lacks many resources necessary to respond to disasters.